Conventional surface-mounting technologies, as are often used in the manufacture of electronic circuits, involve the use of surface mounted devices (SMDs) of increasingly limited dimensions. SMDs are typically installed using computer-controlled automatic “pick and place” type machines with one or more picking and placing heads, which collect the components from suitable feeders and deposit them in a selected position on a printed circuit board or the like.
To prepare the surface mounted devices for collection from their packaging, feeders are often used. Briefly, the feeders open the packages and locate the devices or components at a position necessary for collection by a positioning head.
Of the numerous packaging methods available today, the type most widely used are those which utilize reels of tape. Specifically, the tape is fed in a forward direction by holes punched in the tape. The feeder then separates and winds up the film that was applied to the tape previously to cover recesses containing the surface mounted devices or components.
Generally speaking, two approaches have been developed for feeding the tape forward and retrieving feed the tape forward and retrieve the film. The first is to drive the tape forward by stepwise rotation of a gear wheel; and the second is to use a system of linear actuators. In gear wheel delivery systems, levering devices are commonly used to rotate the gear wheel and, in turn, feed the tape carrying the surface mounted device forward, while simultaneously operating a system that retrieves the film. Such systems are typically operated by pneumatic actuators or, in some cases, electronic actuators.
As for linear delivery systems, they generally a linear electronic actuator, which drives a carriage assembly, complete with retractable pins holes in the tape, thereby entraining the tape with the carriage assembly, and then disengaging therefrom at the beginning of the assembly's return stroke. Such solutions have been used for both single feeders, i.e., where the tape is installed on a separate delivery device, and multiple feeders, i.e., where several tapes are housed by the same unit and a common actuator is used to drive them forward with a system for selecting only those tape(s) that have been programmed for delivery.
While gear wheel and linear delivery type feeder systems have been found useful, the highly complex configurations that are necessary to achieve high operating precision often makes these systems costly to produce and operate. Gear wheel type feeder systems, in particular, have been found further disadvantageous in requirina that the wheel be able to engage tapes of different thicknesses about an arc of a circle, i.e., that some degree of slack must be allowed between the diameter of the tooth and a hole in the tape. Frequently, however, this presents problems with positioning repeatability when different tapes are used. Moreover, where a machine with single-actuating feeders must perform multiple pickups, that is, when the machine's pickup heads descend simultaneously onto a number of exposed surface mounted devices, a mechanical adjustment system is necessary to align the respective feeders. Therefore, in an apparatus with gear wheel type multiple feeders, an adjuster must be provided on each wheel to guarantee the precision needed for multiple pickups.
As for linear delivery multiple feeders, a mechanical housing structure is usually provided with a linear electronic actuator driving a carriage assembly having a plurality of retractable pins, i.e., that rise and fall due to the effect of respective electromagnetic actuators. Selective engagement of the pins allows only the required tapes to move forward along with the carriage assembly. After forward motion, the actuated carriage assembly then returns to a resting position. In this type of feeder, the film covering the surface mounted device is lifted away from one side to enable the device or component to be picked up. The film then exits from the front of the feeder, still attached to the tape, which is now empty on the other side. In practical terms, as the tape advances, it encounters a shaped blade that severs the film from the tape along one side thereof, raising it sufficiently to expose the surface mounted device. Although helpful, this arrangement increases significantly the dimensions and structural complexity of the feeder, while failing to eliminate the risk of tape movement. In addition, using this system, feeding the tapes has been found considerably more complicated. Such system is also considered sensitive to any differences in the way the film is attached to the tape due to manufacturing defects or aging of the adhesive.